ARSENOTUNGSTIC  ACID  AS  AN 
ALKALOID AL  REAGENT 


BY 


EDWIN  ROBERT  LITTMAN 


THESIS 

FOR  THE 

D E G R E E O F KACHE  L O R O F SCI  E N G E 

IN 

CHEMISTRY 


COLLEGE  OK  LIBERAL  ARTS  AND  SCIENCES 

UNIVERSITY  OF  ILLINOIS 


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I0?^u 

Wl"5 


ro 


UNIVERSITY  OF  ILLINOIS 


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Mav  24  192P 

- L I92 

THIS  IS  TO  CERTIFY  THAT  THE  THESIS  PREPARED  UNDER  MY  SUPERVISION  BY 

E_l_'J^r__PpJbejrt__L.i  t_t  n lanri 

ENTITLED  Arsenotunget i c Acid  as  an  Alkaloidal  Reagent. 


IS  APPROVED  BY  ME  AS  FULFILLING  THIS  PART  OF  THE  REQUIREMENTS  FOR  THE 


DEGREE  OF 


Pack  el  or  of  Science  in  Cherrist-rv. 


Instructor  in  Charge 


HEAD  OF  DEPARTMENT  OF 

K.'i  ri'i  no 

n j us..  . 


■ m 


ACICN  0 V/LEDGrBL/ENT 


I wish  to  take  this  opportunity 
of  expressing  my  sincere  thanhs  to  Dr. 
George  Denton  Beal,  who,  by  his  good  will 
and  invaluable  assistance  has  made  this 
inves tigat ion  «.  success* 


Digitized  by  the  Internet  Archive 
in  2015 


https://archive.org/details/arsenotungsticacOOIitt 


HISTORICAL  OUTLINE 


Many  complex  metallic  acids  yield  precipitates  with  organic 
bases.  The  best  known  example  is  the  precipitation  of  an 
ammonium  salt  of  phosphomolybdi c acid,  (ME^JgPO^.lSMoO^, 
when  ammonium  molybdate  is  added  to  a solution  of  phophoric 
acid,  as  the  first  step  in  the  determination  of  phosphorus 
from  practically  all  sources.  The  use  of  phosphornolybdic  acid 
has  since  that  time  been  extended  to  the  precipitation  of  more 
complex  bases.  Ph<£jjho tungstic  acid  has  been  used  to  a much 
greater  extent  in  this  way  than  has  phophomolybdic  acid.  The 
especial  value  of  phopho tungstic  acid  lies  in  its  use  in  the 
separation  of  the  protein  and  non-protein  forms  of  nitrogen,  as 
a substitute  for  the  copper  hydroxide  reagent  of  Stutzer.1 

p 

Bertrand  has  prepared  a series  of  silico- tungstic  acids 
of  which  one  form  of  the  silicc-duodeci tungstic  acid,  4K£0,  SiQg, 

' 7 : 

lEWOg,  2ZRgQ,  has  been  used  successfully  by  the  Chapin  method 
for  the  determination  of  nicotine.  Further  studies  of  silico- 
tungstic  acid  as  an  alkaloids!  reagent  have  been  made  by  Beal 
and  Peterson  and  by  Bueh  and  Beal^  • These  reagents  have 
shown  so  much  promise  that  it  has  been  decided  to  study  the 
behavior  of  other  complex  metallic  acids,  including  the  arseno- 
tun  stic  acids,  with  particular  reference  to  their  availability 
as  precipitating  reagents  for  alkaloids. 


« 


, 


_ o_ 

Chemical  literature  yields  little  on  the  subject  of 
arseno tungstic  acids*  Among  the  references  to  the  preparation 
of  various  forms  of  the  acid  so  far  mention  has  only  been  made 
twice  to  the  reactions  of  arseno tungstic  acids  with  organic 
compounds.  These  are  to  the  work  of  S.R.  Benedic  t*  and 
Morris  Macleod  on  the  reaction  between  arseno tungstic  acid 
and  uric  acid.  Arseno tungstic  acid  has  been  suggested  as  a 
reagent  for  the  determination  of  uric  acid,  based  upon  the 
reducing  action  of  the  uric  acid  on  the  tungsten.  It  was 
found  that  uric  acid  reduced  the  arseno tungstic  acid  to  "tungsten 
blue".  From  this  has  been  developed  a colorometric  method  for 
uric  acid.  The  reaction,  however,  does  not  depend  upon  the 
formation  af  a complex  molecule  containing  the  compounds.  In 
neither  of  the  two  articles  above  was  any  attempt  made  to 
isolate  the  acid  or  any  of  its  salts.  The  authors  state  that 
the  composition  of  the  acid  was  unknown.  In  1888  an  article 

a 

was  published  by  Gibb  on  the  preparation  of  arseno tungstic 
acids  according  to  the  method  of  Fr  emery.  Gibbs,  in  his  own 
work  obtained  a salt  of  the  following  composition:  lo'.VOg .As^O^. 
6AggO  11H  0.  The  method  of  Gibbs  is  as  follows:-  To  an 
aqueous  solution  of  arsenic  acid  add  freshly  precipitated 
barium  tungstate,  followed  by  sulphuric  acid  to  decompose  the 
barium  tungstate.  Filter  the  mixture  and  evaporate  on  the  water 
bath  until  crystals  just  form.  Remove  the  dish  and  allow  to 
cool.  The  precipitate  is  a mixture  of  two  acids  alpha  and  beta. 


_ „ 


, 


. 


-3- 


Dissolve  this  precipitate  in  boiling  water.  Add  Potassium 

chloride  to  form  the  potassium  salts.  A precipitate  should 

separate  immediately.  Allow  Hie  solution  to  cool,  when  yellow 

prisms  should  deposit.  As  soon  as  this  occurs  decant  the  liquid. 

The  two  products  so  obtained  must  be  recrystallized  until  pure. 

The  first  precipitate  is  the  alpha  and  the  second  the -beta  salt. 

The  formulae  are:  alpha  ASgO;.  .9 W0r/  • 14HgO 

beta  As  0 _ . 18 W0f . .XH  0 
2 5 3 2 

Since  1888  no  satisfactory  method  for  the  preparation  of 
an  acid  of  definite  composition  has  been  published.  It  is  true 
that  quite  a number  of  acids  have  been  prepared,  but  there  is 
doubt  as  to  their  composition,  yields  and  methods  of  preparation. 
With  but  one  exception  the  preparation  of  the  acids  involved 
such  proceedures  as  fractional  crystallization  to  separate  the 

Af 

various  compounds  formed.  Zehrman^  in  1900  published  a paper 
on  the  preparation  of  an  arseno tungstate  of  definite  composition. 

His  method  is  as  follows:-  To  a saturated  solution  of  sodium- 
tungstate  add  "syrupy"  arsenic  acid  until  the  solution  is 
distinctly  acid,  then  one  half  as  much  again,  finally  add 
solid  ammonium  chloride  to  precipitate  the  ammonium  arseno tungs tat  . 
The  product  must  be  purified  by  repeated  salting  out.  It  has 
the  formula  3(UH4)20.  ASgO~.  181/0,,.  14H20. 

This  method  was  used  as  a starting  point. 


-4- 

THEQRETIOAL  CONSIDERATION. 

There  is  no  definite  theory  to  account  for  the  combination 
of  arsenic  acid  and  a tungstate  to  form  a complex.  In  view  of 
this  lack  the  condition  of  the  experiments  must  be  closely 

4 

followed  in  order  to  duplicate  results.  The  method  of  Hehrman 
was  modified  in  an  attempt  to  get  better  yields  of  the  pure  salt. 
The  modification  changed  only  the  method  of  precipitation. 

Instead  ox  saturating  the  solution  with  ammonium  chloride  and 
immediately  filtering  the  product,  the  salt  was  added  until  a 
precipitate  just  formed  and  then  allowed  to  stand.  At  the  end 
of  twenty  four  hours  a very  crystalline  precipitate  will  have 
been  deposited.  This  precipitate  is  a pure  salt,  as  purification 
by  salting  out  v/ith  ammonium  chloride  twice  gave  no  changes  in 
the  analysis. 

When  an  attempt  was  made  to  analyse  the  salt  for  arsenic 
many  difficulties  had  to  be  overcome  before  concordant  results 
could  be  obtained.  The  arsenic  v/as  precipitated  as  magnesium 
ammonium  arsenate,  but  even  after  three  precipitations  the 
ignited  residue  showed  the  presence  of  tungstic  oxide  (WQ_). 

An  electrolysis  of  a solution  of  the  ammonium  arseno tungstate 
caused  violent  "popping"  but  no  liberation  of  arsine.  This 
"popping"  and  the  fact  that  the  salt  changed  color  but  did  not 
decrepitate  at  100°  0.  led  to  a further  investigation  as  to  its 
physical  properties.  The  salt  was  placed  in  a dilatometer  and 
the  uulL  heateu.  slowly  xo  11^°  heigth  of  the  column 


, 


* 


-5- 


(Mijol)  was  read  for  each  degree  rise  in  temp era ture.  The 
curve  (.Figure  I.)  shows  that  there  is  a transition  point  at 
97°  - 98°  C.  At  study  of  the  changes  in  crystal  structure 
further  advances  the  probability  of  meta-stability.  A sample 
of  the  dry  salt  when  placed  on  a heated  microscope  (Figure  3) 
stage  changes  in  color  from  yellow  to  green  as  soon  as  the  temp- 
erature reaches  the  transition  point,  but  the  change  is  crystal 
structure  is  not  so  rapid.  If,  however,  a drop  of  water  is 
added  to  the  sample  on  the  stage  the  crustal  change  occours  as 
soon  as  the  water  has  evaporated.  Figure  two  shows  the  original 
salt  (a)  and  after  treatment  wi  th  water  and  heat  (b). 

The  failure  of  the  arsenic  precipitation  can  be  laid  to 
the  meta  stable  compound  being  present  to  some  extent  if  we 
assume  that  the  meta  stable  compound  will  not  give  up  its  arsenic 
as  readily  as  the  stable  material. 

It  was  then  decided  to  decompose  the  complex  by  reducing 
the  arsenic  and  distilling  the  arsenous  chloride  (AsOl^).  The 
most  effective  reducing  agent  found  was  titanous  chloride 
(TiClg).  Hydrogen  sulfide  reduces  the  compound  and  precipitates 
arsenous  sulphide  (As^S^)  only  under  pressure  and  at  high  temp- 
erature. Sulfur  dioxide  has  no  effect.  Zinc  and  hydrochloric 
acid  reduces  the  arseno tungstate  but  wi th  no  evolution  of  arsine, 
(AsH^).  Electrical  reduction  partly  deposits  metallic  arsenic 
but  does  not  liberate  arsine.  The  accompanying  sketch  shov/s 

the  type  of  apparatus  used.  The  distillate  should  not  come  in 
contact  with  any  rubber  because  of  the  presence  of  sulfur  therein. 


F,s.3 


jQeacQSh 


5 Yea 


m 


C/ear  drawn  fletf 


AsCIs  Distillation  FtasR 


Ha  Ccls 


B ottom  of  F\a,  sM 


Q 


round  Joint 


m imm 


-6- 


The  results  of  the  arsenic  analysis,  by  precipitation,  are 
probably  low,  as  five  precipitations  were  made  to  free  it  from 
tungsten. 

As  previously  stated  there  are  only  two  references  to  the 
reactions  of  arseno tungstic  acid  with  organic  compounds  and  both 
of  these  refer  to  uric  acid  only.  The  present  inves tigation  v/as 
undertaken  in  the  hope  that  the  arsenic- tungsten  combination  would 
behave  in  the  same  manner  as  the  silico- tungsten,  phospho tongs ten, 
and  phospho- molybdenum  compounds.  In  order  to  test  the  arseno- 
tungstate,  qualitative  analyses  were  made  upon  quinine,  quinidine, 
chincholine,  and  cinchonidine.  Other  organic  nitrogen  compounds 
were  also  used  &nd  the  results  recorded  in  the  following  table. 

Compound  Formula  Reaction 

Note:  + reaction 


Quinine 


Quinidine 

+ 

Chinchonine 

+■ 

Cinchonidine 

■h 

£ Styryl 

3 Benzoyl  amino 

4 tuinazolone 

/yH  ♦ 

1 ! 9 -CH*  CK  O 

"-NH-CGO 
c 

— 

0 


t 


. 


■ 


-7- 

. ^ H 

Acetanilide  Q N -CQGH^ 


p-Brom 

H 

N - COGH- 

A 

Acetanilide 

0 

Br 

p-Nitro  ethyl 

COGKs 
* -C2H5 

Acetanilide 

0 

ho2 

Ethyl 

Acetanilide 

N - COCH„ 

0'C2H5  3 

— 

Phenacetin 

(V°  °2E5 

V'~  HHOOOHg 

— 

Isobutyl 

Alcohol 

GHS- 

° ^ CK-CE  OH 

GH  * 2 

o 

— 

Secondary 
Butyl  alcohol 

„OH 

CH1XCH0CH  - GH 
B 2 3 

— 

Pyafcidine 

o 

| 

4- 

Quinoline 

oo 

4- 

HpG 

4° 


OH, 

O' 

m 


'GE 

CH 


a 


2 

2 


4- 


Piperidine 


. 


-8- 

Phenyl  amino 
Propionic  acid 

'm2. 

A-  OH  CH^  - 

ky  - co  h 

2 

— 

Trimethyl 

Amine 

(CW 

~h 

p-Nitro  ethyl 

/CmC2H5 

Ana line 

0 

»os 

— 

Anisole 

y\  -QCH* 

o ■ 

— 

Phenyl  amino 
Thiazole 

C S 

C - NHp 

H-  C N 

+ 

2 Styryl 

3 Phene tedyl 

4 Quinazolone 

/V  * C - CH=CH 

- H - o - OCgHg 

Anthraniiic 

Acid 

or 

- co2h 

— 

Uric  Acid 

H - N - C =•  0 

» / 

0 = C C - NHx 

1 H C=0 

H - N - C - HH' 

— 

-9- 


2  Styryl 

ON  V 

N C -CH*CK  - <3 
N - UK  - COCA* 

4 ^uiiiazoxone  "C 

0 


2 Styryl 

3 Amino 

4 Qninazolone 


GHrGK  -<  > 

1!H2 


-h 


-10- 


After  determining  the  extend  of  the  possibilities  in  the 
qualitative  precipitation  of  the  alkaloids,  the  next  step  was  the 
determination  of  the  "factor"  to  be  used  in  quantitative  work. 

The  "factor"  is  explained  by  the  equation:  Wt.  WO^  x "factor" 

Wt.  alkaloid.  The  general  method  for  the  determination  of  the 
"factor"  follows:  Dissolve  the  alkaloid  in  dilute  sulphuric  acid 

with  a slight  excess.  Add  an  excess  of  the  arseno tungstate  sol- 
ution (l  c.c.  .01  gm. ) and  heat  to  boiling,  filter  hot  and  wash 
thoroughly  with  hot  water.  Ignite  the  filter  and  precipitate  in 
a weighed  crucible  at  a low  red  heat  and  weigh  as  tungstic  oxide 
(WOg).  The  "factors"  for  the  four  above  mentioned  aldaloids  are:- 

Quinine  .22565 

Qu ini dine  .30638 

Cinchonine — --  .24268 

Cinchonidine  ----- — .26341 

In  each  case  the  quantitativeness  of  the  precipitation  was 
tested  by  the  standard  methods  of  alkaloid  extraction  after  decomp- 
osition of  the  precipitate  by  sodium  or  potassium  hydroxide. 

The  following  table  shows  the  results. 


Allcalc  id 

Weight  taken 

Weight  recovered 

Quinine 

.01985 

.02005  (Mean) 

Quinidine 

.02505 

.02496 

Cinchonine 

.02497 

.02491 

Cinchonidine 

.02772 

.02764 

-11- 


I&x-ait  IIvlHLT  TAL 

Preparation  of  the  Ammonium  arseno tungstate 

To  200  c.c.  of  saturated,  solution  of  crystallized  sodium 
tungstate  (Na2*704.2Hg0)  ( approximately  85  grams^  add  80  c.c  of  f 
freshly  prepared  arsenic  acid.  (h^AsQ^)  with  constant  stirring. 
The  temperature  of  the  solution  will  rise  appreciably.  Cool  the 
mixture  to  25°  C.  and  add  40  gm.  of  ammonium  chloride  (NR^Cl) 
with  stirring.  Continue  to  stir  rapidly  for  15  minutes  and  allow 
the  mixture  i?o  stand  24  hours.  Pilter  the  mixture  with  suction 
and  centrifuge  the  crystals  until  dry.  The  compound  prepared 
in  this  way  needs  no  further  purification. 

Several  trials  were  made  using  commercial  arsenic  acid  ( 8O/0) 
but  a discolored  product  always  resulted.  The  arsenic  acid  used 
was  prepared  as  follows*.-  To  500  c.c  of  concentrated  nitric  acid 
(C.P.)  add  arsenous  oxide  (AsgOgJin  10  gm.  portions  with  stirring 
until  no  further  reaction  takes  place.  Pilter  through  an  asbeston 
mat  and  use  as  soon  as  possible.  The  above  reaction  proceeds 
as  follows :- 

2H  0 As  A 2HN0  2H  AsO  NO  NO 

2 2 0 O 0 4 2 

ANALYSIS  of  the  Salt 

Ignite  a sample  ( .2  - .5  gm. ) at  the  lowest  possible  red 

The  residue  is  ifYO^. 


heat  to  content  weight 


-12- 


Tun^sten 


Sample 

.1449 

.1765 

Crucible  WO,, 
5 

10.0905 

9.5952 

’ 1 along 

9.9675 

9.4461 

WO* 

.125 

.1491 

84.8$  84.5$ 

Pisco  a sample  ( .5  - 1.0  gm. ) in  a distilling  flask  (See 
sketch)  and  add  100  c.c  of  hydrochloric  acid  (20 $) . Shake  until 
the  material  is  dissolved  then  add  50  c.c  of  titanous  chloride 
solution  (15$).  Distil  the  solution  in  a current  of  cydrogen 
chloride.  Neutralize  the  distillate  with  solid  potash  (KOH)  using 
phenolphthalein  as  indicator.  Just  acidify  with  hydrochloric 
acid  and  again  neutralize  with  sodium  bicarbonate  (NaliGO-)  and 
add  5 gm.  in  excess.  Titrate  this  solution  with  standard  iodine 
using  starch  as  an  indicator. 

Arsenic 

Sample  .5488  .1252 

C.c.  I soln( .1668)  1.15  .47 

As  0 ($)  5.52$  5.50$ 


The  ammonia  was  liberated  with  sodium  hydroxide  and  distill- 
ed in  a Kjeldahl  apparatus. 

Ammonia 


Sample  2.4058 

C.c.  acid( .1055)  25.70 

C.c.alkali( .0971)  .00 


2.6769 
57.0 
7.62 
5 • QO/b 


(hh4)2o 


2.9355a 


-13- 

From  the  above  analysts  the  following  ratios  were  obtained :- 

(1)  AsgC^WOg  1:24.18 

(2)  (EE4)20:As205  5:78:1 

(3)  Ho0:As  0_  32.2:1 

2 2 5 

These  ratios  show  the  following  formula  for  the  ammonium 
arseno tungstate:  4(UE4)20.As20&.24W0^.52E20.  The  specific 

gravity  of  the  salt  was  determined  by  displacement  of  ligroin 
and  was  5.343  referred  to  water. 


Determination  of  the  "factors" 

Dissolve  the  alkaloid  Salt  in  water  (or  just  enough  10  $ 
sulfuric  acid  if  the  free  alkaloid  is  used)  and  add  5 c.c.  of 
10; a sulfuric  acid.  To  this  solution  add  an  excels  of  arseno- 
tungstate  solution  and  heat  to  boiling.  Filter  hot  and  wash 
the  precipitate  thorougly  Tilth  boiling  water.  When  the  excess 
water  has  drained  off  place  the  wet  filter  in  a weighed  crucible 
and  ignite  very  slowly  . never  allowing  the  paper  to  more  than 
glow.  Vi/hen  the  paper  has  been  thoroughly  charred  ignite  at  a 
faint  red  heat  to  constant  weight  (WOg).  The  following  results 
were  obtained. 


Data  on  Factors 
quinine 

fuinine  Hydrochloride  .01S85 

Dish  and  Residua  — - — - — — 25*6411 
Dish  alone  -- — ---------------  25.6250 

Residue  .0161 

Factor  .2256 


.01985 

22.4086 

22.3920 

.0166 


I , 

, 

« 


. 


* 


-14- 


Qu  ini  dine 

Quinidine  Sulphate 
Dish  and  Residue 
Dish  alone 
Residue 

Factor  .3064 


.025035 

10.1455 

10.0565 

.0890 


.025035 

9.5619 

9.4925 

.0894 


Cinchonine 

Chinchonine  Hydrochloride  .02497 
Dish  and  Residue  9.5755 

Dish  alone  9.4828 

Residue  .0927 

Factor  .24268 


.02497 

9.5316 

9.4390 

.0926 


Cinchoni&ine 

Cinchonidine  Hydrochloride  .02772 
Dish  and  Residue  9.5329 

Dish  alone  9.4394 

Residue  *0935 

Factor  .2634 


.02772 

9.6789 

9.5852 

.0937 


Qualitative  Tests  on  Organic  Compounds 


The  compounds  were  dissolved  in  a solvent  common  to  the 
reagent  and  the  compound  and  acidified  with  dilute  sulfuric 


acid 


- 15- 


Fur  the  r Studies  on  Ars eno- tungs ti c 
Acid 

The  ars  eno  tungstate  when  treated  in  aquous  solution  with 
ammonium  oarhonate  precipitates  a white,  crystalline  product. 

This  material  was  not  analysed  for  arsenic  but  showed  83.7 % 

W03. 

If  the  mixture  of  arsenic  acid  and  sodium  tungstate  is  sat- 
urated with  ammonia  (MHg)  a white  amorphous  compound  precipitates. 
It  c 021  tains  ab 09. t 66. 5>&  WOg. 

The  tungsten  in  the  £41'703  compound  is  not  precipitated  with 
acids  until  the  arsenic  is  removed.  This  indicates  a stable 
complex. 

When  electrolyzed  so  as  to  theoretically  release  the  arsenic 
as  arsine  a solution  of  the  ars eno tungstate  turns  blue  but  gives 
no  arsine.  When  the  same  solution  is  treated  in  the  same  way  but 
with  the  cathode  in  a porus  cup  metallic  arsenic  is  partially 
precipitated. 

Sulphur  dioxide  will  not  reduce  tie  arsenic  or  tunsten. 
Hydrogen  sulphide  causes  reduction  only  at  100°  0. , and  under 
pressure; (a  pressure  flash  was  used). 

Iron  salts  cause  a blue-green  coloration  in  an  acid  solution 


of  the  sal t 


-16- 

SUMMARY  of  WORK. 


A rapid  method  for  the  preparation  of  an  ammonium 
arseno tungstate  has  been  devised.  The  salt  has  a definite 
composition,  4( .As^O^.  24  WO  .32H  fl>. 

The  ammonium  arseno tungstate  precipitates  certain 
definite  alkaloids.  Other  organic  nitrogen  compounds 
are  precipitated  by  the  reagent,  but  only  when  apparently, 
the  basicity  reaches  a definite  point. 

A method  has  been  devised  whereby  alkaloids  may 
be  quantitatively  determined  through  the  use  of  ammonium 
ar s eno  tungs  ta  t e . 

Some  properties  of  the  ammonium  arseno tungstate  have 
been  investigated  and  the  results  recorded. 


. 

• 

• 

* 

- 

• 

• ) 

' . . ' 

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B I BL I QGRAPHY 

* J.G •Drummond-  Observations  on  the  Phospho tungstates  of 

Certain  Bases  and  Amino  Acids. 

Bioehem.  J.  IB,  5 - 24  (1918) 

1.  Stutser Untersuchungen  ueber  die  quantitative  Bestim- 

mung  des  Proteinstichstoff es  und  die  Trennung 
der  Pro teins toff e von  anderen  in  Pflarijjen 

vorkommenden  Sticks toffverbindungen. 

J.  f.  laudwirtjischoft  1880,  28,  103; 

1881,  29,  473; 

1886,  34,  151 

2.  Bertraud  — Comptes  Rendus  128  - 742  - 1899 

Bull.  Soc.  Ghim.  2,434  (3)  (1900) 

3.  Chapin  — The  determination  of  Nicotine  in  Nicotine 

Solutions  and  Tabacco  Extracts. 

Bull.  No.  133—  U.S.Dep’t  Ag.  Bur.  of  Animal 

Husbandry. 

4.  Beal  and  Peterson  - Silico  Tungstic  Acid  as  an  Alkaloidal 

Reagent.  Thesis  - U.  of  Illinois  1920 

5.  Buck  and  Beal  - Extraction  of  Alkaloids  by  Means  of 

Immiscible  Solvents.  Thesis.  U.  of  111.  1921 

6.  S.R. Benedict  - Uric  Acid  in  Blood 

J.  Biol.  Ghem.  LI  - 1. 

7.  J.L.  Morris  and  A.G.Macleod  - Golorometric  Deterimation  of 

Uric  acid  in  Blood.  J.  Biol.  Chem.  1-1 

8.  Gibbs  - Annalen  245,  1888,  50 

9.  Kehrman  - Zt.  Anorg.  Ghem.  22,  1900,  290 


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GMRRAL  REh'ERWGlSS 


Graelin  -ICraut 
Berichte 
Zt.  Zryst* 

ii  ii 

Rosooe  and  Schorlemer 
Ab  egg 
0.  Dommer 
Ho ffinan- Lexicon 
Chem.  Abst. 


3/2-  594,  595,  602,  695 

IV,  1834,  296 

21,  1893,  313 

22,  1893,  307 

V. 2,  p.  1061 
3/3 

V.2,  p.616 
V.15,  Ho.  1,  p.145 


